Citroen showed off its Airflow 2L concept at the Paris Motor Show, a C4 Cactus designed to get 118 mpg.
Josh Miller/CNET

PARIS -- European automakers' obsession with achieving minimum fuel usage for 100 kilometers of travel has resulted in a new concept here at the Paris Motor Show: the Citroen C4 Cactus Airflow 2L. Based on a standard production model Cactus, Citroen has refitted the car with new lightweight components and technologies to achieve 2-liters of gasoline per 100 kilometers, or approximately 118 mpg.

The C4 Cactus is a four-door hatchback with a low roof height, making for a sporty look with good interior practicality. Citroen specified a number of changes to this model for the Airflow 2L concept.

The Airflow 2L concept uses a hybrid drivetrain, but instead of electricity, compressed air contributes to power. A gasoline-electric hybrid drivetrain converts waste kinetic energy from braking and coasting into electricity, powering an electric motor to drive the wheels. Citroen's HybridAir drivetrain uses waste kinetic energy to compress air, which in turn can help drive the wheels. Compressed air tanks are lighter and less expensive than batteries.

Further helping fuel economy, Citroen shaved 220 pounds from the production car for the concept. The body makes use of composite plastics, high-strength steel and aluminum to retain structural integrity but lighten the overall car. One specific innovation is a composite panoramic sunroof with built-in UV protection.

Aerodynamic improvement makes for a big part of the Airflow 2L's fuel economy. Side flaps and an extended rear spoiler reduce drag at the rear. Front air intakes on the bumper and flaps on the wheels automatically adjust to improve air flow. The 19-inch wheels are narrow, to reduce rolling resistance.

Unrelated to fuel economy is a new window washer system, with fluid jets in the tips of the windshield wipers. Citroen says this feature uses 30 percent less washer fluid. The side of the concept and the standard C4 Cactus features what Citroen calls AirBumps, which are small, air-filled chambers that protect the doors from dents.

Some of these modifications may be too expensive or impractical for a production vehicle, but successful testing of the concept will likely see some find their way into future models. The 118 mpg figure would be based on European fuel economy testing -- US EPA testing tends to produce lower results, but this model still may be close to 100 mpg.